The present invention relates to static power switching systems, and more specifically to static power inverters which utilize a parallel resonant LC circuit and have load coupling to the inductor through its magnetic field for power take off. Furthermore, the present invention relates to a novel method of driving the resonant circuit of a static power switching system to enhance the efficiency of energy transfer to the load, particularly in such inductive switching applications as induction heating and cooking.
Static power switching systems include both inverters and converters. An inverter circuit is used to convert a dc input to an ac output. Subsequent rectification of the inverter ac output results in dc-to-dc conversion, or a converter circuit. In each type of switching system, a controlled switching element for the dc supply is required. Present day switching systems, particularly inverters, utilize semiconductor devices, for example, silicon controlled rectifier (SCR) and power transistor, for the switching element.
Although parallel resonant circuit static inverters providing a sinusoidal output are known, they are less favored than a series circuit static inverter. Particularly for resistive loads, series circuit inverters have heretofore been predominantly utilized because a series inverter is self commutating and current limited by the series capacitor.
Static power inverters have found application in induction heating equipment wherein an electrically conductive material is subjected to a varying magnetic field which produces an eddy current loss and a hysteresis loss therein so that the temperature of the material increases. While induction heating is found in many industrial uses, it is also finding increasing usage in kitchen ranges for cooking food.